smtpd_delay_reject (default: yes)
Wait until the RCPT TO command before evaluating $smtpd_client_restrictions, $smtpd_helo_restrictions and $smtpd_sender_restrictions, or wait until the ETRN command before evaluating $smtpd_client_restrictions and $smtpd_helo_restrictions.

This feature is turned on by default because some clients apparently mis-behave when the Postfix SMTP server rejects commands before RCPT TO.

The default setting has one major benefit: it allows Postfix to log recipient address information when rejecting a client name/address or sender address, so that it is possible to find out whose mail is being rejected.